One way roller clutches typically include a cage that provides the basic structural foundation for the clutch. The cage includes a series of circumferentially spaced roller pockets, formed by axially spaced, annular side rails interconnected by axially extending cross bars, each of which pockets contains an individual roller and spring. The cage is installed by various techniques between a cam race and a coaxial pathway race. The pathway race, which is often, though not always, the inner race, has a simple cylindrical surface or pathway, on which the rollers freely roll and on which the cage pilots. The cam race is more complex, and includes a series of circumferentially spaced, asymmetrically V shaped notches, separated from one another by semi cylindrical, co radial bearing surfaces. Each V or saw tooth shaped notch has a long, shallow angled side sloping in one direction, called a earn ramp, against which a spring loaded roller is continually urged by an individual spring that pushes off the cage. The selective wedging or jamming of the rollers against the cam ramps locks the races together when they attempt to relatively rotate in one direction, but allows free wheeling in the other relative direction. Each notch also has a much shorter and steeper, oppositely sloped side, sometimes called a cam hook, which simply provides a quick surface transition back down to the adjacent semi cylindrical bearing surface. Since the cam hook has no necessary function per se, other than to serve as a transition from one surface to another, it could, theoretically, have any shape that was practical to machine. It is typically flat, however.
A use has been found for the cam hook in terms of how the cage is installed to, and properly oriented relative to, the cam race. Cage installation to the cam race is an operation that is generally carried out before the pathway race is pushed coaxially inside of the cam race. A common cage to cam race assembly method is the so called "twist lock" technique, detailed in co assigned U.S. Pat. No. 4,712,661. The plastic cage is molded with radially outwardly extending reaction ears that are short enough to pass through the peaks of V shaped notches, thereby allowing the cage to be freely pushed axially inside the cam race. The cage position that allows this pass through is angularly offset from the cage's final position. After pass through, the cage is then twisted back to its final installation position, causing a sloped surface of the reaction ears to abut the cam hooks. As the cage is twisted back, a flat face of the reaction ears simultaneously slides over and "locks" to the outside faces of the cam race, which prevents the cage from shifting axially on the cam race. The inner pathway race is added last by the so called "ringing on" method, with an axial push and simultaneous twist in the same direction that the cage was twisted. This compound motion of the pathway race causes the cylindrical pathway to concurrently roll all of the rollers slightly up the cam ramps, that is, toward the cam hooks, thereby compressing the roller springs. Afterward, the force of the compressed springs pushing the rollers off of the cage and against the cam ramps also continually pushes the reaction ears back against the cam hooks, thereby keeping the cage in its proper angular orientation on the cam race. Clearly, an absolute requirement of the twist lock technique of cage installation is that the profile of the outer edges of the cage side rails not closely match the profile of the V shaped notches. If it did, then there would the enough cage clearance to allow the cage to pass through the cam race in an angularly offset orientation.
Other methods of installing, orienting, and retaining the cage to the cam race do exist, such as that disclosed in co assigned U.S. Pat. No. 4,995,489, in which the cage is molded with a shape that causes it to twist itself automatically as it is pushed onto the cam race. Another method is shown in co assigned U.S. Pat. No. 5,062,512, in which the cage is pushed straight in without a twist, but has a special design that allows it to effectively shrink in circumference and then re expand so as to snap into a central groove in the cam race and retain itself without reaction ears. In both designs, however, there is significant radial clearance between the cage and the cam ramps. A full profile cage, that is, one in which the outer edges of both side rails of the cage closely matched the exact shape of the cam ramps with little or no clearance, would inherently have to be installed with just a simple, straight on push fit, with no angular offset or twisting. As such, a separate means, such as snap rings, might have to be used to retain the cage to the race, which is obviously not preferred over a self retaining cage.
Another function of the cage, beyond acting as a framework to hold the rollers and springs, is to keep the races radially spaced apart during clutch operation in a near coaxial relation, sometimes referred to as concentricity control. This is typically accomplished by providing arcuate sections in the cage, known as beating blocks, that pilot on the pathway and closely fill the radial space between the pathway and the semi cylindrical portions of the cam race. The bearing blocks keep the races concentric, or, at least, limit the degree of running eccentricity to an acceptable level. The beating blocks should be radially solid, or nearly so, in order to provide good load support between the races. When a clutch is designed with more rollers and cam ramps within a given circumference, in order to give it a higher torque capacity, the interstitial space between the cam ramps that is available for bearing blocks inevitably becomes narrower, limiting the load support that beating blocks can provide. An alternative for providing concentricity control would be a full profile cage, that is, a cage having axially opposed side rails with outer edges that closely matched the entire profile of the cam race, as well as an inner edges that piloted closely on the pathway. If full profile cage side rails could also be made radially solid and uninterrupted, then they could provide a large measure of the inter race load support that bearing blocks typically provide. In addition, such solid, full profile cage side rails, if they could be practically manufactured, would provide stronger roller pockets with better resistance to impact from the ends of the rollers. Another possible benefit would be improved retention the lubricant that is often pumped between the cage side rails through feed holes bored through the pathway race. Full profile, small clearance pocket side rails would do a better job of keeping the lubricant around the rollers, reducing wear. Lubricant retention is poor if there is a large radial clearance between the edges of the cage side rails and the race surfaces. Enhanced lubricant retention for typical large clearance cages must currently be provided with extra seals added on to the cage, as is shown in co assigned U.S. Pat. No. 4,714,803.
The real world impediments to making a hypothetical roller clutch cage with full profile, radially solid side rails are many, in terms of manufacturing, installation, and clutch operation after assembly. As far as manufacturing, it is almost a requirement now that cages be plastic injection moldings, and, preferably, one piece moldings made by the so called axial draw or by pass molding method. In a cage designed to be produced by the pass method, only two axially parting molds, with no internal inserts or radially moving slides, are sufficient to form the entire cage. There are many existing cage designs that achieve that objective, one of which can be seen in co assigned U.S. Pat. No. 4,712,661, a basic design that is repeated and modified in many other patents. The hallmark of all one piece, by pass moldable cage designs is cage side rails that are not radially continuous or solid, so that they do not radially overlap or block the opposite side rail as viewed in the axial direction. To achieve that basic relationship, one side rail must occupy less than the entire radial space between the races, while the opposed side rail occupies the remainder of that radial space, or some portion of the remainder. In contrast, radially solid, full profile cage side rails would completely radially overlap, and it would be physically impossible to by pass mold them with two axially parting molds. To make a plastic cage with radially solid side rails would require either that it be molded in one piece with inserts and slides, or that it be molded in multiple pieces that were assembled together after molding. One such multi-piece cage is shown in co assigned U.S. Pat. No. 4,054,192, in which each pocket is separately molded and then snapped together like links in a bracelet. This, of course, maximizes the possible number of separate pieces, which is not a desirable option for ease of manufacture or assembly. Even that design, however, cannot provide full profile side rails, because it, too, relies on the twist lock cage assembly technique described above. The other option for solid, strong, full profile cages is to provide two stamped metal side rails that are held together by separate cross rails, as shown in co assigned U.S. Pat. No. 4,787,490. Even with this design, the side rails do not conform very closely to the cam profile. The reason for this is that there is no circumferential flex or give in metal side rails, so a true full profile, closely conforming side rail could bind up on the cam race during cage installation, if tolerances in the side rail shape were only slightly off.
Another problem with a true full profile cage side rail, even if it were to be made of more flexible plastic, is the temperature expansion and contraction differential that exists between plastic and the metal clutch races during clutch operation. Some provision should be provided to allow the plastic cage to compensate by expanding and contracting, so as to conform itself to the metal clutch races. Cage side rails that were simply the plastic equivalent of full profile metal side rails would not be able to expand and contract freely. Several one piece, by pass molded cage designs do include structural features that allow temperature differential compensation. These are typically slots or other relieved areas that allow the pockets to flex back and forth relative to one another. Examples may be seen in co assigned U.S. Pat. Nos. 4,712,661, 4,830,463 and 4,850,463. None of these designs, however can have full profile, radially solid cage side rails, because of the very fact that they are one piece by pass moldings.
To summarize, what the plethora of existing cage designs outlined above fails to provide in a single design is a plastic roller clutch cage with strong, full profile, radially solid side rails, which is by pass molded and easily assembled with a minimal number of pieces (meaning two), which can be easily installed to the cam race after assembly without binding, which retains itself to the cam race after it is installed, and which will conform itself after installation to the races.